Getting terminate called after throwing an instance of 'std::length_error'

I am getting this above error and I am unable to debug the cause for it. Can anyone help me with this (what's causing this error)?

Problem Statement: Finding Longest Common Prefix

Source: https://leetcode.com/problems/longest-common-prefix/

Code(Using Divide and Conquer):

class Solution {
public:
    string common_prefix(string left, string right){       
        int minim = min(left.length(), right.length());
        for (int i=0; i<minim; i++){
            if (left[i]!=right[i]){
                return left.substr(0, i);
            }
        }
        return "" ;
    }
    string dap(vector<string>& a, int l, int r){
        if (l==r) return a[l];    

        int mid = (l+r)/2;
        string left = dap(a, l, mid);
        string right = dap(a, mid+1, r);
        return common_prefix(left, right);
    }
    string longestCommonPrefix(vector<string>& strs) {

        
        return dap(strs, 0, strs.size());
        
    }
};

Traceback:

Runtime Error
terminate called after throwing an instance of 'std::length_error'
  what():  basic_string::_M_create